Investigating if psychosis-like symptoms (PLIKS) are associated with family history of schizophrenia or paternal age in the ALSPAC birth cohort

Psychosis-like symptoms (PLIKS) occur in about 15% of the population, but it is unclear to what extent PLIKS share aetiological mechanisms in common with those for schizophrenia. We examined whether the presence of PLIKS was associated with a family history of schizophrenia (FH-SCZ), or with advancing paternal age, using data from 6356 children in the ALSPAC birth cohort who participated in a semi-structured PLIKS interview at 12 years of age. We found no evidence of association between FH-SCZ and suspected or definite PLIKS (adjusted OR=0.94, 95%CI 0.44, 2.00; p=0.880). There was weak evidence that advancing paternal age was associated with increased PLIKS (adjusted OR per 10-year age increase=1.23, 95%CI 0.99, 1.55; p=0.058). Although not a priori hypotheses, family history of depression (adjusted OR=1.28, 95%CI 1.04, 1.57; p=0.018), and younger maternal age (adjusted OR per 10-year age increase=0.62, 95% CI 0.47, 0.82; p<0.001) both showed stronger evidence of association with suspected or definite PLIKS. Overall our findings provide little evidence that these established risk factors for schizophrenia show a similar relationship with PLIKS, suggesting that the presence of PLIKS is unlikely to be a strong marker of early expression of the pathology underlying schizophrenia. Whether future studies of PLIKS will increase our understanding of mechanisms underlying the development of schizophrenia, or prove useful in prediction of this disorder, remains to be seen.